Mechanism behind solution color change due to pH change

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Discussion Overview

The discussion revolves around the mechanism behind the color changes observed in an organic polysaccharide solution due to pH variations. Participants explore the structural aspects of polysaccharides and their relationship to color changes, specifically focusing on a polysaccharide solution that transitions from colorless at pH ≤ 6 to yellowish-green at pH 11.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks literature on the mechanism of color changes in polysaccharide solutions due to pH changes, noting specific observations from their experiments.
  • Another participant emphasizes the need for specificity regarding the type of polysaccharide to provide a more accurate response, suggesting that the presence of hydroxyl groups may influence sensitivity to pH changes.
  • A participant mentions their use of hemicellulose xylan from corn core and expresses interest in understanding the mechanism behind its color change from colorless to yellowish-green as pH increases.
  • Questions are raised about the purity of the xylan and whether substituents affect its behavior, along with inquiries about the method used to alter pH.
  • One participant proposes a potential analogy to the yellowing of paper due to oxidation of lignins, suggesting that a similar chemical reaction might be at play in the polysaccharide solution.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as multiple viewpoints and questions remain regarding the specifics of the polysaccharide in question and the underlying mechanisms of the observed color change.

Contextual Notes

Limitations include the lack of specific information about the polysaccharide structure and the conditions under which the experiments were conducted, as well as the unresolved nature of the proposed mechanisms.

Who May Find This Useful

Researchers and students interested in organic chemistry, polysaccharide behavior, and the effects of pH on chemical properties may find this discussion relevant.

Baho Ilok
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I would like to ask for somebody to point me in the right direction - any literature I could read - regarding the mechanism behind color changes that an organic solution undergoes due to changes in pH. I am not referring to organic indicators or dyes, specifically. I have observed in my experiments that a certain polysaccharide solution is colorless at pH ≤ 6 and gradually turns yellowish-green as pH is increased to 11 at room temperature. I was wondering if there is an explanation for this phenomenon that relates to the compound's structure (i.e. presence of certain functional groups).

Thanks!
 
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Well there are plenty of types of Polysaccharides. You'll have to be more specific in order for people to give you a good answer.
But I think it is obvious from the basic chemical structure of Polysaccharides with a lot of hydroxyl groups that it is sensitive to higher region of pH.
 
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HAYAO said:
You'll have to be more specific in order for people to give you a good answer.
In my experiments, I use the hemicellulose xylan from corn core. I know of its structure but the mechanism by which its solution changes from colorless to yellowish-green from acidic to basic pH is what I would like to know. Thanks!
 
Baho Ilok said:
In my experiments, I use the hemicellulose xylan from corn core. I know of its structure but the mechanism by which its solution changes from colorless to yellowish-green from acidic to basic pH is what I would like to know. Thanks!
Okay, is the xylan "pure" xylan? Or are there substituents on it? I don't know what xylan looks like when taken from corn core.

Also, what are you using to change the pH?
 

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